Restore compatibility with vagrant 1.4

The v2 plugin API was subtly changed in Vagrant 1.5 to accept command
options such as `primary: false` as a second argument to `command` but
it remains unsupported in previous Vagrant versions. This workaround
backports the support albeit by simply dropping the given options.

Bug: 71878
Change-Id: Id67a7d96be812ac6ac453a4675ddc2f056300ef4